Estimation of the orientation distribution of short-fiber composites using ultrasonic velocities

A method for estimating the orientation distribution function (ODF) of short-fiber composites using measured ultrasonic velocities is presented. The method is based on the coupling of (i) a forward micromechanics model of the effective ultrasonic velocities of the textured composite in terms of the coefficients in an expansion of the ODF in generalized spherical harmonics, (ii) ultrasonic measurements of the velocities, and (iii) an inversion algorithm to obtain the coefficients of the ODF from the measured velocities and the forward model. The approach is used to determine the ODF coefficients for a transversely isotropic short-fiber SiC/Al metal-matrix composite. The ODF coefficients obtained by inversion of ultrasonic velocities agree reasonably with those obtained from neutron-diffraction pole figures. Corresponding elastic constants predicted with these coefficients also agree well with independently measured elastic constants.